In my more charitable moods, I merely pity the headmaster I had between ages 8-13. I can't comment on his strengths or weaknesses as a husband (doubtless faithful and loving), a father (doubtless an inspiration to his children) or a soldier (doubtless fought bravely for his King in WW2). I can't even really comment on him as a teacher - I'm pretty sure he taught me history in my last year but it's just a blank, apart from one thing which I'll come to. But he taught me other things in other ways ...
His ability to walk into a room where absolutely no one was misbehaving, identify at least two offenders and punish them was staggering. (It was never just one offender, because - mantra #1 - "It takes two to make a fight.") Nor could anyone else who had witnessed the event, or lack of it, bear testimony for their friends. Mantra #1a - "Do you really expect me to believe that?", with the very strong implication that you should stand down now, or join them in whatever punishment he had devised.
So he taught me that where theory (or ideology, or dogma) and fact disagree, fact wins every time.
He taught me that standing by your beliefs if your beliefs are wrong and lack any factual basis is not actually worthy of respect. I have never subscribed to the "you have to admire the courage of his convictions" theory. Not if he's a pillock, you don't. And the more you use sheer authority to steamroller your view of reality through in the face of all fact and reason, the more contemptible and pathetic you look.
He would move goalposts, or abolish goalposts altogether. Conditions would be set for X to happen; the conditions would be met and often exceeded; but X would not happen because he simply changed his mind. So he taught me to let your yay be yay and your nay be nay, and he taught me to look ahead. If it looks like you're going to make it a nay anyway, just say so.
He taught me that you can base your authority on fear, or respect, but respect really is better.
And sadly he taught me two things on which we can both actually agree. (By which I mean, on purpose and by direct example.)
The one thing I remember from his history lessons is a throwaway remark I made about "primitive times", by which I think I meant around the 17th or 18th century. His margin note was: "careful, in many ways they were more civilised than us." An unexpected shaft of open-mindedness, which is maybe why it stuck.
And the other was mantra #2, "any fool can be uncomfortable". School expeditions were always well equipped, with everyone dressed appropriately for the weather of the day. Which is why, having just come back from a pleasant post-prandial stroll around the park with Best Beloved, warmly muffled against a biting wind in coat and scarf and hat and gloves, I feel moved to write this.